Method of forming glass bonded heads



Feb. 20, 1968 GJMANDERS 3,369,292

METHOD OF FORMING GLASS BONDED HEADS Original Filed Nov 215, 1962 2Sheets-Sheet l 1% FIG.3 F|G.4 H65 19 1s 9 1s I 16 a INVENTOR.

GODEFRIDUS J. MANDERS AGE NT 1968 G. J. MANDERS METHOD OF FORMING GLASSBONDED HEADS Original'Filed Nov. 25, 1962 2 Sheets-Sheet 2 FIG.10 FIG."FI,G .12

INVENTOR.

GODEFRIDUS J. MANDERS AGEN United States Patent 3,369,292 METHOD OFFORMING GLASS BONDED HEADS Godefridus Johannes Mand'ers, Emmasingel,Eindhoven,

Netherlands, assignor to North American Phillips Company, Inc., NewYork, N.Y., a corporation of Delaware Original application Nov. 23,1962, Ser. No. 239,759, now abandoned. Divided and this applicationSept. 7, 1965, Ser. No. 509,232 Claims priority, applicationNetherlands, Sept. 20, 1962, 283,790 3 Claims. (Cl. 29-603) ABSTRACT OFTHE DISCLOSURE A method of manufacturing transducer heads by forming aplurality of parallel V shaped projections along the face of a block offerrite material, forming an auxiliary groove at either end of the blockafter the last projection, placing a spacer element abutting the face ofthe block and having a bent portion extending down into the auxiliarygroove, forming another plurality of grooves at right angles to thefirst, glass bonding a mating ferrite block onto the original block,cutting the block between each projection, and cutting the remainingplates into as many separate plates as there are right angle grooves.

This application is a division of Ser. No. 239,759, filed Nov. 23, 1962and now abandoned.

This invention relates to magnetic transducer heads for recording,reproducing and/or erasing magnetic recordings. It relates in particularto such heads adapted to transduce video signals in a very narrow trackof a magnetic record carrier, wherein the head comprises at least twomagnetic circuit elements composed of sintered oxidic ferromagneticmaterial separated by a useful gap; the gap is filled with nonmagneticmaterial which serves to protect the walls of the circuit elementsforming the useful gap and also mechanically bonds the two circuitelements together. The invention also relates to a method ofmanufacturing such transducer heads.

Heads of the above type, especially when used for transducing videosignals, must have gaps which are extremely short, of the order of from1 to 2 microns, and also extremely narrow, of the order of 0.2 mm.; thevery narrow dimension is necessary since often a number of tracks arelocated beside each other. In addition, in order to permit the recordingof a large quantity of information per unit of surface area of thecarrier, the distance between the tracks must be small.

It is clear that such a transducer head composed of sin tered materialand having dimensions as narrow as indicated is comparatively weak;there is therefore a danger that both the gap walls and the edges of thehead are apt to crumble away. In addition, the fact that the head isnarrow means that the bonding of the two circuit elements is weak,especially since the depth of the gap may also be very small in order tomaintain the magnetic reluctance of the gap as great as possible. It isknown to manufacture such narrow heads with small gap widths by grindingboth sides of the upper surface of a comparatively wide head at an angleuntil the desired width is obtained and then filling with non-magneticmaterial the portion which was ground away, the non-magnetic materialbeing of such a nature that it adheres to the sintered material of thecircuit elements. However, this method of manufacture is a difficultone; in addition it has been found in practice that considerable wearcan occur in heads manufactured in this manner.

The magnetic transducer heads according to the invention are notdifiicult to manufacture and have good wearing properties in operation.According to one aspect of the "ice invention, a magnetic transducerhead is provided having two magnetic circuit elements composed ofsintered oxidic ferromagnetic material and bonded together as notedabove, both elements being of substantially the same thickness, with oneelement being pointed so that the gaplimiting surface of this elementhas a much smaller width than the gap-limiting surface of the otherelement; the portion of the head which includes the small gap-limitingsurface is filled with a filling material having approximately the samemagnetic and mechanical properties as the material in the gap.

According to one embodiment of the invention, the filling material atthe small gap-limiting surface is the same as the material in the gap.This embodiment has the advantage that both the coefiicient of expansionand the resistance to detrition of the filling material are exactly thesame as those of the material in the gap; thus, the side walls of thebearing surface are protected as well as the gap walls, and the samedetrition exists throughout the bearing surface of the head.

According to a further embodiment of the invention, the narrowgap-limiting surface preferably is located in the center of theparticular circuit element and the filling material extends on bothsides of this element.

The invention also includes a method of manufacturing a magnetictransducer head of the above type. According to one aspect of themethod, a first plurality of parallel grooves are formed in the majorportion of a side face of either of two substantially identical blocksof sintered oxidic ferromagnetic material; a narrow portion of the sideface parallel to these grooves is retained, The grooves are separated byprojections having a V-shaped crosssection, the tip of the V beingflattened with the fiat portion being located in the side face, thewidth of the flat portion being equal to the desired width of the gap.In addition an auxiliary groove having an approximately rectangularcross-section is provided in each of said narrow portions or in thecorresponding position in the side face of the second block, saidauxiliary grooves extending in parallel with said first plurality ofgrooves. Then either of the two side faces is provided with a secondplurality of grooves which are at right angles to the first pluralityand have a substantially semi-circular cross-section, the number and theposition of the second plurality of grooves being determined by thedesired number and the shape of the heads, after which the block havingthe auxiliary grooves is provided with spacing members in the form offoils having a thickness equal to the desired gap length, a part of thefoils being located in the auxiliary grooves. After this, both blocksare placed against each other with the interposition of a glass platewhich has a thickness greater than the desired gap length and then theresulting assembly is heated under pressure to a temperature above themelting temperature of the glass. A-fter melting and cooling, theassembly is divided into plates by grinding or sawing parallel to theprojections, the surface of separation between two plates is always inthe center between two projections, the resulting plates being dividedby a similar operation at right angles to the direction of theprojections into a number of parts equal to the number of said secondplurality of grooves; each part comprises one portion of such a groove,and the resulting parts are provided with coils and a bearing surface.

There are various ways according to the invention in which the signalcoil space may be made. According to one embodiment of the invention, anadditional groove having a substantially rectangular cross-section isprovided in the block adjacent to and in parallel with each of saidsecond plurality of grooves, said additional groove being used as thecoil space. According to another embodiment of the invention, the coilspace is provided in each finished part by ultra-sonic machining in amanner such that a portion of the glass filling the semi-circular grooveis removed. In order to form an easy outlet for the excess glass, theenclosed air, and possibly formed gas, narrow grooves which are parallelto the projections may be provided in the bottoms of the groovesseparated by V- shaped projections and/or in the corresponding positionin the side face of the second block.

The side faces of the block comprising the V-shaped projections may beground beforehand, so that these side faces may be used as referencesurfaces during manufacturing. However, it is desired to establish theposition of the glass plate accurately; according to an embodiment ofthe invention the grooves having the semi-circular crosssection may beprovided in the second block, the glass plate in this case beingprovided with ridges fitting these grooves.

For correct centering of the assembly, a deep groove at right angles tothe projection may be provided in both blocks and the glass plate mayconsist of two parts, a centering beam being provided in the twocorrespondingly located grooves before compressing and heating theassembly, said beam being of the same material as the material of theblocks, and each glass plate being placed on either side of the beam.

According to a further embodiment, the position of the semi-circulargrooves and the place where the plates are physically separated intoparts are chosen so that the distance in each part between an edge of apart and the most adjacent principal limiting is equal to the desireddepth of the gap of the head.

In order that the invention may readily be carried into effect, certainembodiments thereof will now be described more fully, by way of example,with reference to the accompanying drawing, in which:

FIG. 1 shows a finished head on an enlarged scale;

FIG. 2 is a plan view of the head as shown in FIG. 1 also on an enlargedscale;

FIG. 3 shows a block of sintered oxidic ferromagnetic material providedwith grooves;

FIG. 4 shows a glass plate;

FIG. 5 shows a block of the same material and the same dimensions as theblock shown in FIG. 3;

FIG. 6 shows a combination of the parts shown in FIGS. 3, 4 and 5;

FIG. 7 shows the assembly of FIG. 6 provided with lateral grooves;

FIG. 8 shows a plate which is cut from the block shown in FIG. 7;

FIG. 9 shows another embodiment of the block shown in FIG. 3;

FIG. 10 is a glass plate separated into two parts and provided withridges;

FIG. 11 shows a centering beam;

FIG. 12 shows a block similar to that shown in FIG. 5;

FIG. 13 shows a combination of the parts shown in FIGS. 9, 10, 11 and12;

FIG. 14 shows a plate which is cut from the block shown in FIG. 13;

FIG. 15 shows the plate of FIG. 14 after further processing; and

FIG. 16 shows a head manufactured from the plate shown in FIG. 15.

Referring now to FIGS. 1 and 2, a magnetic transducer head is shownwhich is particularly useful for recording and reproducing videosignals, the head consisting of two magnetic circuit elements 1 and 2which are separated by a useful gap 3. The gap 3 which has a length of,for example, 1 /2 microns, is filled with glass or other nonmagneticmaterial which bonds the members 1 and 2 together. The head has arounded bearing surface 4 along which a magnetic record carrier such asa tape is adapted to move. The element 2 is pointed and V-shaped, the V-shape having a flat surface 5 the two ends of which define the gapwidth. Non-magnetic material 6 is provided to fill out the portions ofelement 2 which were cut away to form the V-shape in a manner such thatthe total width of the element 2 at all parts thereof is the same as thetotal width of the element 1. The nonmagnetic material 6 is preferablythe same as that which fills the gap 3. Below the active part of the gap3 a cavity 7 is provided which is also filled with glass and serves forsupporting and strengthening the part of the head located above it. Inaddition the head includes a rectangular coil space S for receiving theturns of a coil (not shown), which turns are provided on the outside ofthe head in grooves 9. Grooves 9a serve for connecting the head. Such ahead is comparatively strong; both the gap surfaces and the surfaces ofthe V-shaped part of element 2 are supported, so that no crumbling cantake place during operation; in addition, sufficient support is providedfor the lower part of the gap. Since the same material is placed both inthe gap and at the surfaces of the V-shaped part and serves as asupport, and the coefficient of expansion and the resistance todetrition of this material may be chosen to conform with the material ofthe head itself, a homogeneous assembly is obtained.

One manner of manufacturing such a head will now be described. In FIG.3, reference numeral 10 denotes a block of sintered oxidic ferromagneticmaterial hereinafter termed ferrite. In this block 10 which comprisesfour ground side walls, grooves 11 are formed in one side wall as shown.These grooves are separated by projections 12 which are V-shaped. thetip of the V having a flat portion 13. This fiat portion 13 is locatedin the plane of the side wall and has the same width as the desiredgapwidth 5 in FIG. 2. When forming the grooves 11, small surfaces 14 areretained; grooves 15, having a substantially rectangular cross-section,are provided in the surfaces 14 approximately in parallel with theprojections 12. Finally, grooves 16 having approximately a semi-circularcross-section are ground into the projections 12; the grooves 16 haveaxes extending at right angles to the projections 12. The determinationof the position and the number of these grooves 16 will be describedbelow. A second block 17 also com-- posed of ferrite (FIG. 5) hasapproximately the same di-- mensions as the outer dimensions of block10. A glass plate 18 (FIG. 4) has the same length and width as theblocks 19 and 17 and has a thickness which somewhat exceeds the desiredgap length. With a gap length of for eX- ample 1% microns the thicknessof the glass plate is ap proximately 5 microns.

When manufacturing the magnetic recording heads as shown in FIGS. 1 and2, metal foils 19 having the same thickness as the desired gap lengthare first placed on the block 10 at the four corners as shown. A bentpor tion 20 of this foil is supported in the groove 15. Foils composedof mica may also be used; while shown in FIG. 3 at the corners only, thefoils may extend throughout the length of the groove 15. Then the glassplate 18 is placed on the block 10 after which the block 17 is placed onplate 18, the assembly of FIG. 6 resulting from these steps. The groundside walls of the block 10 serve as reference surfaces. The assembly ofFIG. 6 is now heated to a temperature above that of the meltingtemperature of the glass plate 18; during the heating step, pressure isexerted at right angles to the blocks on both exposed sides thereof. Assoon as the glass has melted, the grooves 16 also become filled withglass. The foils 19 serve as spacing members; the foils are thereforecomposed of a material whose melting temperature is higher than themelting temperature of the glass. After cooling the assembly, the blockis provided with grooves 9 and- 2a on either side (FIG. 7) and is thensawed into plates along the dotted lines 21, the plates being indicatedby reference numeral 22 in FIG. 8. Plate 22 is now sawed into two partsalong the dotted line 23 and provided with a rounded bearing surface 4and, by preferably ultrasonic machining with a coil space 8, so thatfinally, a head is obtained as shown in FIGS. 1 and 2.

It can be seen that the material in the gap on either side of theV-shaped portion and the material which serves for supporting the gapwalls is the same. It is clear that the position of the grooves 16 isdetermined by the ultimately desired gap depth as appears from FIG. 8.More than two grooves 16 may be provided as desired; the number dependsupon the number of heads to be manufactured from the plates 22 and uponthe width of the blocks and 17 and the glass plate 18. The distancebetween the grooves 16 in case of more than two grooves willconsequently not be equal to one another in most of the cases.

The grooves and 16 may be provided in the block 17 as shown in FIG. 5 indotted lines instead of in the block 10. In this case it is necessarythat both blocks 10 and 17 have the same length and width and that theside faces of both blocks are readily polished so that accuratelylocated reference surfaces are available.

The method described has the advantage of being simple and of providinga plurality of heads whose dimensions may be determined accuratelybeforehand. Also heads may be obtained having different dimensions, ifsuch is desired, by varying the distance between adjacent projections 12(and flat portions 13).

In FIGS. 9 to 16 another embodiment of the method is shown formanufacturing the heads shown in FIGS.

1 and 2. In FIG. 9, a ferrite block is indicated by reference numeral 24and is again provided with grooves 11, projections 12 and flat portions13. Grooves 15, 9 and 9a are also provided, and foils 19 are put inplace in the same manner as in FIG. 3. In addition, a groove 25 isground in the block 24. A centering beam 26 is shown in FIG. 11 and thiscentering beam is fitted into groove 25. The glass plate used for thisembodiment consists of two parts 27 (FIG. 10) which are each providedwith ridges 28 as shown. A ferrite block 29 (FIG. 12) also includes agroove 30 in which half of the centering beam 26 is adapted to fit.Grooves 31 are provided in block 29; they correspond to the groove 16shown in FIG. 3 and are adapted to receive the ridges 28. In this case,the side faces of the two blocks 24 and 29 need not be polished. Thecentering beam may also be manufactured from ferrite; its use ensuresthat when placing the two blocks 24 and 29 on each other the correctposition of both blocks relative to each other is maintained. Afterheating at a suitable temperature under pressure, the block shown inFIG. 13 is sawed into plates along the dotted lines 32; the plates areshown in FIG. 14. After providing the coil space 8 and after roundingthe two side faces 33 and 34 by means, for example, of ultrasonicmachining, the plates may be sawed into two elements each forming a headsection. It is clear from FIG. 15 that a bearing surface in this case isformed on the outside of the plates 35. However, this depends only onthe position of the grooves 31 and the ridges 28. Of course it is alsopossible to provide the grooves 31 nearer to the center and in this casethe bearing surfaces 33 and 34 are ground on the other side.

The coil space 8 may also be provided beforehand by grinding a groove ofapproximately rectangular crosssection in the blocks on the one side ofthe groove 16 or 31 and in the other block in a corresponding position.In this case, some glass will enter the coil space but this will beinconsequential during winding.

In order to allow the air or gases formed during the manufacture toescape easily during the heating of the blocks under pressure, grooves36 (shown by dotted lines) may be provided in the bottom of the grooves11 and/ or in corresponding positions of the second block. Thesegrooves, together with the grooves 15, may receive the excess glass.

It is of course also possible to provide another block against the sideface of the block 17 and 29 respectively, which is not in contact withthe block 10 and 24 respectively, the additional block being providedwith grooves 6 11 on either side, and to close this latter block withthe interposition of the glass plate 18 or 20 and a block 17 and 29respectively, so that more heads may be obtained in one heating step.

As compared with the known methods for manufacturing heads havingextremely short gap length and very narrow gap widths, the methoddescribed has the advantage that it requires only one heating cycle, asa result of which the possibility of making mistakes is minimized. Inaddition, the methods according to the invention are very suitable formass production of magnetic recording heads, since in principle a largenumber of heads may be manufactured simultaneously.

While the invention has been described with respect to specificembodiments, various changes and modifications will be readily apparentto those skilled in the art without departing from the inventiveconcept, the scope of which is set forth in the appended claims.

I claim:

1. A method of manufacturing magnetic transducer heads, comprising:forming a first plurality of parallel grooves in a side face of oneblock of sintered oxidic ferromagnetic material, each pair of saidgrooves being separated by a V-shaped projection, the tip of eachprojection being flat and extending co-planar with the plane of saidside face, the width of each flat portion of said projection being equalto the desired gap width of the head, retaining a narrow strip of saidside face on either side of said first plurality of grooves, forming anauxiliary groove having a substantially rectangular cross-section ineach said narrow strip, each auxiliary groove extending parallel withsaid first plurality of grooves, forming a second plurality of groovesextending through said projections at right angles to said firstplurality, said second plurality of grooves having a substantiallysemi-circular cross-section, placing spacing members, each being of athickness equal to the desired gap length and each having an offsetportion, upon the multi-grooved side face of said block with the spacersabutting said side face and respective offset portions engaging anauxiliary groove, placing a glass plate having a thickness greater thanthe desired gap length against said spacing members, placing a secondblock of sintered oxidic ferromagnetic material against said glassplate, heating the resulting assembly under pressure to a temperatureabove the melting temperature of glass, allowing the assembly to cool tothereby render the assembly bonded, and separating the assembly intoplates, each plate being parallel to and including a projection, andthen dividing the plates thus obtained at right angles to the directionof the projections into as many parts as the number of said secondplurality of grooves.

2. A method of manufacturing magnetic transducer hea-ds comprising:forming a first plurality of parallel grooves in a side face of oneblock of sintered oxidic ferromagnetic material, each pair of saidgrooves being separated by a V-shaped projection, the tip of eachprojection being flat and extending co-planar with the plane of saidside face, the width of each flat portion of said projections beingequal to the desired gap width of the head, retaining a narrow strip ofsaid side face on either side of said first plurality of grooves,forming a second plurality of grooves extending through said projectionsat right angles to said first plurality, said second plurality ofgrooves having a substantially semi-circular crosssection, forming atleast one auxiliary groove having a substantially rectangularcross-section in a side face of a second block of sintered oxidicferromagnetic material, the side face of said second block havingsubstantially the same cross-section as said one block, said auxiliarygroove extending parallel with said first plurality of grooves when saidside faces are superimposed, placing spacing members, each being of athickness equal to the desired gap length and each having an offsetportion, upon the multigrooved side face of said block with the spacersabutting said side face and respective offset portions engaging anauxiliary groove, placing a glass plate having a thickness greater thanthe desired gap length against said side face of said first block,placing said spacing members against said glass plate, heating theresulting assembly under pressure to a temperature above the meltingtemperature of glass, allowing the assembly to cool to thereby renderthe assembly bonded, and separating the assembly into plates, each platebeing parallel to and including a projection, and then dividing theplates thus obtained at right angles to the direction of the projectionsinto as many parts as the number of said second plurality of grooves.

3. A method of manufacturing magnetic transducer heads, comprising:forming a first plurality of grooves in a side face of one block ofsintered oxidic tferromagnetic material, each pair of said grooves beingseparated by a projection, the tip of each projection beingsubstantially flat and extending co-planar with the plane of said sideface, the width of each fiat portion of said projection beingsubstantially equal to the desired gap width of the head, retaining anarrow strip of said side face on either side of said first plurality ofgrooves, forming an auxiliary groove having a substantially rectangularcrosssection in each said narrow strip, each auxiliary groove extendingparallel with said first plurality of grooves, forming a secondplurality of grooves extending through said projections at right anglesto said first plurality, said second plurality of grooves having asubstantially semicircular cross-section, placing spacing members, eachbeing of a thickness equal to the desired gap length and each'havin-g anoifset portion, upon the multigrooved side face ofsaid block with thespacers abutting said side face and respective offset portions engagingan auxiliary groove, placing a glass plate having a thickness greaterthan the desired gap length against said spacing members, placing asecond block of sintered oxidic ferromagnetic against said glass plateheating the resulting assembly under pressure to a temperature above themelting temperature of :glass, allowing the assembly to cool to therebyrender the assembly bonded, and separating the assembly into plates,each plate being parallel to and including a projection, and thendividing the plates thus obtained at right angles to the direction ofthe projections into as many parts as the number of said secondplurality of grooves.

References Cited UNITED STATES PATENTS 2,032,003 2/ 1936 Clause 65-43 X2,707,694 5/1955 Standring 156-295 X 3,187,410 6/1965 Duinker et al29l55.5 3,187,411 -6/1965 Duinker et a1. 29l55.5 3,258,542 6/1966 Pfost29l55.5 X

JOHN F CAMPBELL, Primary Examiner.

R. W. CHURCH, Assistant Examiner.

